Process for production of dimensionally stable polyester yarn for highly dimensionally stable treated cords

Abstract

Polyethylene terephthalate yarn is prepared by spinning under very high-stress conditions wherein oriented-crystalline undrawn yarns are obtained. Selection of process parameters yields a partially oriented semicrystalline undrawn yarn with a crystallinity of 16 to 24 percent and a melting point elevation of 14° to 22° C. which is drawn to produce the resulting unique combination of properties: (A) a terminal modulus of at least 20 g/d, (B) a dimensional stability defined by E 4 .5 +FS<11.5 percent, (C) a tenacity of at least 5 grams per denier, (D) a melting point elevation of 14° to 22° C., preferably 17° to 20° C., and (E) an amorphous orientation function of less than 0.75. The resulting treated tire cord unexpectedly provides high ultimate elongation and high toughness in combination with improved dimensional stability.

What is claimed is: 
     
       1. A process for production of a drawn polyethylene terephthalate yarn which translates to a highly dimensionally stable tire cord, comprising: (A) extruding a molten melt-spinnable polyethylene terephthalate having an intrinsic viscosity of 0.8 or greater through a shaped extrusion orifice having a plurality of openings to form a molten spun yarn,   (B) solidifying the spun yarn gradually by passing the yarn through a solidification zone which comprises (a) a retarded cooling zone comprising a heated gaseous atmosphere, and (b) a cooling zone adjacent said retarded cooling zone wherein said yarn is rapidly cooled and solidified in a blown air atmosphere,   (C) withdrawing the solidified yarn at sufficient speed to form a crystalline, partially oriented yarn with a crystallinity of 16 to 24% and a melting point elevation of 14° to 22° C., and   (D) hot drawing the yarn to a total draw ratio between 1.2/1 and 2.5/1.   
     
     
       2. The process of claim 1 wherein the melting point elevation is 17° to 20° C. 
     
     
       3. The process of claim 1 wherein the steps A, B, C, and D are performed in a continuous integrated spin-draw process. 
     
     
       4. The process of claim 3 wherein the melting point elevation is 17° to 20° C.